Table 2. Reaction Energies (in eV) Corresponding to the Conformational Isomerization of [Fe(CN)₅(NO)]^2– Complex Calculated with Different Methods and 6-31G Basis Set.

	ΔES→Fa	ΔES→Rb
B3LYP	1.77	1.91
CCSD	1.72	2.03
CASSCF(14,15)	1.63	1.23
NEVPT2(14,15)	2.30	1.34
AC0(14,15)	2.34	1.18
AC(14,15)	2.20	1.15
DMRG-SCF(16,16)	1.83	1.18
AC0(16,16)	2.18	1.46
AC(16,16)	2.14	1.38
icMRCISD(4,4)	1.90	1.44
CCSD-in-B3LYP	1.27	1.85
CCSD-in-HF	1.36	2.12
DMRG-in-B3LYP	1.92	1.17
DMRG-in-PBE0	1.89	1.27
DMRG-in-HF	2.01	1.44

^aΔE_S→F denotes the energy difference between flat (F) and standard (S) isomers.

^bΔE_S→R denotes the energy difference between reverse (R) and standard (S) isomers.